A photodiode is a semiconductor component comprising a P-N type junction and having, in particular, the ability to detect radiation in the optical spectrum and convert it into an electrical signal. Photodiodes with reverse bias are used, for example, to detect and measure incident photon fluxes.
Reverse biasing a photodiode actually makes it possible to accelerate free charge carriers due to the effect of an electric field applied in the depletion zone located between n-type doped layers and p-type doped layers. The free charge carriers can acquire sufficient energy to create additional electron-hole pairs. If the reverse bias is sufficient, this produces an avalanche effect, i.e. multiplication of the number of photocarriers starting with a small number of initial photocarriers.
The so-called avalanche photodiode can be used, in particular, to detect incident photon fluxes relatively sensitively and quickly and offers various possible applications including implementing detection focal-planes for active imaging, high-speed detection in the field of telecommunications, spectroscopy, detecting very weak luminous fluxes and even photon counting.
Improving the operating parameters of an avalanche photodiode produces the following results in particular:                amplification of weak currents as well as a low electronic noise factor in order to ensure a good signal-to-noise ratio;        minimisation of the dark current that flows through the avalanche photodiode and contributes towards degradation of the signal-to-noise ratio;        an increase in avalanche gain; and        a reduction in the bias voltage.        
Document EP 1 903 612 proposes a photodiode that has the particular advantage of having a relatively small dark current as well as high gain with low reverse bias without degrading the signal-to-noise ratio of the detector which uses it, especially when detecting infrared radiation. This photodiode comprises a stack of semiconductor layers having a first conductivity type and a region that extends transversely relative to the planes of the layers and having a conductivity type opposite to the first conductivity type so as to form a P-N junction with the stack.
However, this photodiode does not offer very good performance. In fact, despite having an acceptable sensitivity and response time, it may be necessary to provide cooling for the photodiode, especially when it is used at high temperature, because of the extrinsic doping of the stacked layers. In addition, the dark current increases as the operating temperature of the photodiode rises, thereby limiting the sensitivity of the photodiode when operating at high temperatures.
Also, to the extent that it is difficult to achieve perfectly pure crystals, a doped semiconductor material contains not only extrinsic dopants, i.e. those associated with the deliberately incorporated impurities, but also residual dopants that are associated with intrinsic defects, for example structural defects or chemical impurities which cannot be eliminated when manufacturing the material. The presence of these two types of defects causes recombination in materials, diminishes the lifetime of the minority carriers, which is already shortened by the Auger effect, and contributes towards the dark current, especially when the photodiode is used at a high temperature.
In order to overcome this background, the object of the present invention is to propose a photodiode that is free of at least one of the above-mentioned limitations. More especially, the object of the present invention is to improve the performance of the photodiode according to the prior art and, in particular, to propose a photodiode capable of capturing infrared radiation at high temperatures.